ELECTRON-MICROSCOPIC STUDY OF RETINAS OF MACULAR MICE

Background: Menkes' disease may be due to a lack or deficiency of copp er in various organs. The macular mouse is known as a model for Menkes ' disease. We examined melanin granules in the retinal pigment epithel ium and the activity of cytochrome oxidase, a copper-containing enzyme , in the retinas of macular mice by electron microscopy. Methods: In t he retinas of hemizygote macular mice we demonstrated cytochemically ( oxidative polymerization of diaminobenzidine to an osmophilic reaction product) the activity of cytochrome oxidase. The distribution of mela nin granules in the retinal pigment epithelium related to the activity of another copper-containing enzyme, tyrosinase, was also studied. St ereological methods were applied to obtain quantitative data. Results: In the retinal photoreceptor inner segments of the macular mouse, the mitochondria were more numerous than in normal littermates and they a ppeared swollen. There were fewer melanin granules in the retinal pigm ent epithelium of macular mice than in that of normal littermates. The cytochrome oxidase activity was significantly lower in the macular mi ce than in the controls. Conclusion: Macular mice have lower activity of cytochrome oxidase and fewer melanin granules than do normal mice. Both changes may be related to copper deficiency. These results corres pond to the retinal changes seen in patients with Menkes' disease.